1. Field of the Invention
The present invention relates generally to image recording device, and in particular, the present invention is directed towards image recording device in which images are recorded to a recording medium while the recording medium is nipped and conveyed by a pair of rollers disposed in a conveying path.
2. Description of Related Art
Referring to FIGS. 22 and 23, in a known image recording device, recording paper P is conveyed on to a platen 93 while the recording paper P is nipped between a conveying roller 94 and the pressure roller 95 on the upstream side. When the tip edge of the recording paper P is disposed below a recording head 91, a scanning carriage 92 begins scanning, such that the recording head 91 discharges ink on to the recording paper P. The conveying roller 94 and the pressure roller 95 intermittently are driven based on a predetermined line feed pitch. Each time that the conveying roller 94 and the pressure roller 95 intermittently are driven, the scanning carriage 92 performs scanning, such that the recording head 91 performs image recording. By repeating such an operation, image recording is applied to a predetermined portion of the recording paper P, which is conveyed on the basis of the predetermined line feed pitch. When the tip edge of the recording paper P reaches the conveying roller 94 and the pressure roller 95 on the downstream side, images are recorded on the recording paper P while the recording paper P is nipped by the conveying roller 94 and the pressure roller 95 at the tip edge side and the trailing edge side thereof As the recording paper P moves, the trailing edge of the recording paper P passes through the conveying roller 94 and the pressure rollers 95 on the upstream side, and the recording paper P is conveyed by the conveying roller 94 and the pressure roller 95 on the downstream side. After imaging is complete, the recording paper P is ejected after passing through the conveying roller 94 and the pressure rollers 95.
The conveying roller 94 and the pressure roller 95 abut each other on their roller surfaces, such that a nip region is formed therebetween. When the trailing edge of the recording paper P passes the nip region, the nip force acting between the conveying roller 94 and the pressure roller 95 is released, and a biasing force of the pressure roller 95 is exerted on the trailing edge of the recording paper P, whereby the recording paper P is pushed toward the conveying direction. Due to the biasing force, the recording paper P is conveyed by a predetermined line feed pitch or more, e.g., suffers from so-called skipping. When such skipping occurs, the recording position of the recording paper P is displaced in the sub-canning direction (conveying direction), and in a case of margin less image recording, the resulting recorded image may suffer from non-uniformity or print dropout.
To address this issue, one known control method may be employed to control the conveying roller 94, so as to convey, when the trailing edge of the recording paper P passes through the nip region, the recording paper P by a line feed pitch, which is less than the predetermined line feed pitch by any expected amount of skipping for the recording paper P. Through such control, even when the recording paper P skips, the line feed pitch is not increased, such that the resulting recorded image is protected from print dropout.
Alternatively, another known control method may be employed in which a conveying error is determined through the detection of an amount of skipping of the recording paper P, and the conveying error is corrected. Specifically, the conveying error is determined using the rotation amount of the conveying roller 94 on the downstream side of the conveying roller 94 and the pressure roller 95, e.g., when skipping is observed on the recording paper P, the conveying roller 94 is being rotated more often than is necessary for the predetermined line feed pitch. Thus, the conveying error may be determined from the rotation amount. When the conveying error is determined, instead of normal image recording using the recording head 91 as described above, control is applied so that the recording paper P is conveyed in the opposite direction by the conveying error before the recording head 91 scans. Thus, the resulting recorded image may be protected from non-uniformity or print dropout even when the recording paper P skips.
Nevertheless, the amount of skipping of the recording paper P varies depending on the size, the thickness, the type, or the like of the recording paper P, such that amount of skipping of the recording paper P is not always uniform. For example, as shown in FIG. 23, each conveying roller 94 is provided with four pressure rollers 95 disposed at regular intervals in the axial direction. Each of the pressure rollers 95 is biased toward the conveying roller 94, e.g., via a spring (not shown). The conveying roller 94 and the pressure rollers 95 abut each other on their roller surfaces so that nip regions N are formed therebetween. The biasing forces of the pressure rollers 95 do not always result in the same amount of skipping to the recording paper P, and the amount of skipping observed on the recording paper P varies depending on the image recording device. Moreover, the amount of skipping varies depending on the size, the thickness, the type, or the like of the recording paper P. As such, the amount of skipping of the recording paper P is affected by the pressure rollers 95 and the properties of the recording paper P. Therefore, it is difficult to correct an amount of skipping of the recording paper P using one fixed, estimated value in every image recording device.
To determine the amount of skipping of the recording paper P by the rotation amount of the conveying roller 94, the movement of the recording paper P has to match the rotational movement of the conveying roller 94. This requires applying the biasing force using the pressure rollers 95 for the purpose of bringing the recording paper P in to contact with the downstream conveying roller 94. Nevertheless, because the pressure rollers 95 contact the recording surface of the recording paper J which just was printed upon by the recording head 91, if too much biasing force is applied, a nip mark by the pressure rollers 95 remains on the resulting recorded image. Moreover, to convey the recording paper P in the opposite direction using the amount of skipping as a conveying error, the conveying roller 94 needs to rotate in the opposite direction. This requires control over a drive system with consideration given to backlash between gears of a drive transmission mechanism, making operation of image recording device complicated.